Felting process for making combustible cartridge cases



Nov. 23, 1965 K. F. BEAL ETAL FELTING PROCESS FOR MAKING COMBUSTIBLE CARTRIDGE CASES Filed Oct. 23. 1963 FIG.

acnmgm INVENTORS KEITH F. BEAL ERIK R. NIELSON United States Patent Ofiice 3,218,907 Patented Nov. 23, 1965 3,218,907 FELTING PROCESS FOR MAKING COM- BUSTIBLE CARTRIDGE CASES Keith F. Beal, Chicago Heights, and Erik R. Nielsen, Des

Plaines, Ill., assignors to the United States of America as represented by the Secretary of the Army Filed Oct. 23, 1963, Ser. No. 318,453

2 Claims. (CI. 86-10) This invention relates to, and has as its principal objects provision of, felted combustible cartridge cases and a process for the preparation of the same.

In the known processes for making cartridge cases, difficulties are sometimes encountered when it is desired to form cases with irregularities in design such as beveled edges or the like. Both time and money are required to overcome such diificulties. The present invention pro vides a process for preparing cartridge cases, even those including some irregularities in design, in a rapid and relatively cheap fashion. In addition, the process can be employed to make combustble cases, i.e., cases which are consumed within the firing chamber from such materials as nitrocellulose.

According to the present invention, a cartridge case is manufactured by (1) making up an aqueous slurry of cellulosic or other appropriate fibers, (2) forming fibers from the slurry into a mat (preform) of suitable size and shape, i.e., felting the fibers, and (3) molding the preform into the final shape as by a die at an elevated temperature. When cellulose fibers are employed as the starting material, the final shape (4) can be nitrated as in a sulfuric acid-nitric acid bath or by any other conventional procedure to form a combustible case. When nitrocellulose fibers are used to make up the slurry, the nitration step, of course, is unnecessary.

Apparatus suitable for carrying out the shaping and molding steps of the invention are shown in section in the drawings wherein:

FIGURE 1 is a movable felting mandrel on which the preform can be cast directly from the slurry, the numeral designating the base of the mandrel; 11 a slightly conical head; 12, a channel extending longitudinally through both base and head and through which a vacuum can be drawn; and 13, perforations in head 11 through which water can be pulled by the vacuum;

FIGURE 2 is a molding die on which the molding step can be performed having a base 15, a conical head 16, a channel 17 extending through head, base and side arm 18, and perforations 19; and

FIGURE 3 is a concave die 20 fitting over the head of r the die of FIGURE 2 and shaping the mat during the molding operation.

In practice, a slurry comprising about l2% alpha cellulose fiber is dispersed in water with agitation as necessary. Both the concentration of the slurry and the composition of the fibers are subject to variation as desired. The slurry is contacted with the felting mandrel under vacuum to make a preform and the preform is transferred to the molding die. The concave die is pressed over the preform, the temperature is raised and the mat is molded into a cartridge case blank and dried. Temperatures up to 300 C. or above can be employed with cellulose fibers but in the case of nitrocellulose fibers 165 F. is generally not exceeded. Nitration is, of course, also carried out where nitrocellulose fibers are not employed.

Generally, it is desired to strengthen the cartridge cases felted as above. Strengthening can be accomplished by adding to the felted material an agent such as viscose, a lacquer, a resin or the like. Resins which may be used with the felted cartridge cases include polyvinyl acetate emulsion, polyvinyl acetate polymer, melamine formaldetit] hyde, triazine formaldehyde, acrylic ester, alcohol-soluble nylon, methyl methacylate, polyethylene emulsion, melamine, phenolic resins, polyvinyl butyral, etc. Materials containing sulfur or halogens are usually avoided since these elements tend to produce smoke. These strengthening materials can be incorporated by dipping the preform in a solution containing the same before the molding step is accomplished or, if the preform is not nitrated, after the nitration step.

It has also been found that the strength of the cases can be improved if some cellulose fibers are incorporated in the final product along with the nitrocellulose. The property of combustibility within the firing chamber or tube is retained although some cellulose is in the product. Products containing both cellulose and nitrocellulose are conveniently prepared from a slurry comprising a blend of these materials.

There follow some nonlimiting examples illustrating the process of the invention in more detail.

Example I A mixture of alpha cellulose fibers approximately A; inch long and 25% 5 /2 denier viscose rayon fibers of equivalent length were dispersed in distilled water to form a felting slurry of about /2% fibers. Gentle agitation was employed to keep the fibers in suspension. A hollow felting mandrel was placed under vacuum and immersed in the slurry until a suitable preform of fibers had been deposited. This preform was then transferred to the molding die, placed under vacuum through the side arm, and pressed into final shape with the concave mold at a temperature of about 300 C. The pressed articles were then nitrated by vapor-phase nitration with nitrogen pcntoxide (see below) to a nitrogen content of 13.4%.

Four felted cases prepared as described above were test fired in a .4l0 gauge smooth-bore test gun adapted from a shot gun. In the first test firing, the total combustion mass was 1.646 grams and developed a peak pressure of 32,600 p.s.i. In the second instance, the total combustion mass was 1.854 grams developing a peak pressure of 33,540 p.s.i. All rounds burned completely.

Example II To provide cartridge cases of improved physical strength, a set of preforms was made as described in Example I and dried. After drying, the preforms were slipped over glass rods and dipped into diluted viscose.

The viscose solution was prepared by steeping 50 grams of wood pulp alpha cellulose (rayaceta grade from Rayonier, Inc.) in 18% NaOH for one hour at 21 C. Excess caustic was pressed out to give 185 grams of alkali cellulose which was shredded in a Waring Blendor, sealed in a one quart fruit jar and aged at 21 C. for 65 hours. At the end of that time, 18 grams of carbon disulfide were added, the jar rescaled, and the reaction allowed to continue for 4 hours at 21 C. Excess CS was removed under vacuum and the cellulose xanthate formed was dissolved in 30.4 grams of 50% NaOH and 436 grams of water to give viscose. One part of this viscose was diluted with six parts of water for impregnating the felted cases.

After the cases were removed from the diluted viscose solution, they were wrapped tightly with 40 mesh wire gauze and dried under vacuum at C. The gauze was removed and the viscose regenerated for 15 minutes in a bath containing 9% H 50 and 16% Na SO After being washed free of salts and drying, the cases were well shaped and sturdy. They were then nitrated in a conventional H SO -HNO bath. The nitration caused shrinkage but the cases retained their strength and shape.

3 Example III (A) Two and one-half grams of /2 inch rayon staple fiber, dried under vacuum over phosphorous pentoxide, were placed in a one inch glass tube 10 inches long connected to a nitrogen pentoxide reservoir and to a calcium chloride drying tube. Dry air was passed over the N crystals as they were warmed to room temperature to assist in their sublimation and to carry the vapors through the fibers. The nitration proceeded from one end of the tube to the other, its progress being shown by the appearance of droplets of nitric acid on the fibers and on the walls of the tube. Nitration was continued for about 2 /2 hours. After a thorough wash in cold water followed by four washes in boiling water, the nitrated fibers were vacuum dried. Analysis indicated 13.41% nitrogen. Although the fibers were more brittle than before nitration, they were still fairly soft and flexible.

(B) Nitrocellulose fibers prepared as described above are slurried in water, shaped into a preform on a mandrel, dipped into a dilute solution of a polyvinyl acetal resin and molded on a die at a temperature of up to about 165 F.

Since obvious modifications and equivalents in the invention will be evident to those skilled in the chemcal arts, we propose to be bound solely by the appended claims.

We claim:

1. The process of preparing a combustible cartridge case which comprises:

(1 slurrying nitrocellulosic fibers in water;

(2) sucking the fibers on a shaped perforated mandrel from the slurry until a suitable preform is obtained;

(3) depositing on the preform cellulose from another slurry for additional strength;

(4) removing the preform to a perforated die and pressing a concave cap over said preform to improve the moisture removal through the perforations of the die by a vacuum;

(5) molding and drying the preform into a cartridge case in the die at temperatures up to 165 F. 6 2. The process of preparing a combustible cartridge case which comprises:

(1) slurrying cellulosic fiber in water; (2) drawing the fibers on a shaped perforated mandrel dipped in the slurry by suction from within the man- 10 drel until a suitable preform of fibers is deposited;

(3) removing the preform to a perforated die and pressing a concave cap over said preform to improve the moisture removal through the perforations of the die by vacuum; (4) molding and drying the preform into a cartridge case in the die at elevated temperatures up to 300 C.; (5) nitrating the case after removal from the die by any suitable means to make the case combustible and (6) Cementing the case by means of a viscose solution for additional strength.

References Cited by the Examiner UNITED STATES PATENTS 88,948 3/1869 Ely 10243 313,187 3/1885 Dickerman 86-10 1,859,324 5/1932 Ayerst 162-228 1,907,795 5/1933 Hall 162-228 2,890,615 6/1959 Lefebure 8610 2,947,254 8/1960 Weiss 10243 2,982,211 5/1961 Beal et a1. l0243 3,043,742 7/1962 Chaplin 162-228 3,098,444 '7/1963 Walkey 10243 BENJAMIN A. BORCHELT, Primary Examiner.

SAMUEL FEINBERG, Examiner. 

1. THE PROCESS OF PREPARING A COMBUSTIBLE CARTRIDGE CASE WHICH COMPRISES: (1) SLURRYING NITROCELLULOSIC FIBERS IN WATER; (2) SUCKING THE FIBERS ON A SHAPED PERFORATED MANDREL FROM THE SLURRY UNTIL A SUITABLE PREFORM IS OBTAINED; (3) DEPOSITING ON THE PREFORM CELLULOSE FROM ANOTHER SLURRY FOR ADDITIONAL STRENGTH; (4) REMOVING THE PREFORM TO A PERFORATED DIE AND 